(WEST LAFAYETTE) - Porter County has the 13th-highest carbon-dioxide emissions in the U.S. That's according to a computerized CO2 map developed at Purdue.

The "Vulcan" mapping system shows Porter County putting out $6.3-million tons of CO2 per year. That's barely a third of the number-one county: Harris County, Texas. That's home to Houston and its oil refineries.

Vulcan Project Leader Kevin Gurney notes the top emitters are spread all over the U.S., and make the list for different reasons -- Houston takes the top spot because of industrial smokestacks.

Similarly, three-quarters of Porter County's emissions can be traced to industry, mainly steel mills. But second-place Los Angeles County is there on the strength of automobile exhaust.

Vulcan's data are from 2002, but Purdue plans to expand the map to cover more recent numbers.